The present invention is related generally to the field of semiconductor wafer manufacturing, and more particularly to a cooling system for a semiconductor wafer fabrication apparatus.
During many semiconductor fabrication processes, a semiconductor wafer is cooled by an assembly adapted to provide a supply of coolant, such as helium, for example, to the back side of the wafer (that is, the side of the wafer in contact with the chuck) during the fabrication process. The coolant supply is not always uniform, however, and fluctuating coolant mass flow may exert instantaneous forces on the wafer which overcome the relatively constant force biasing the wafer to an electrostatic chuck. In cases where the net force on the wafer is non-zero, a force differential may cause a portion of the wafer to rise above the chuck; in extreme cases, an abnormally high flow rate of coolant may even cause the entire wafer to move or to be raised off the chuck. These situations cause alignment complications during a fabrication process, and are undesirable.
When uniform contact of the wafer with the chuck is compromised, the apparatus or process chamber will typically sound an alarm through a warning system. This alarm and the subsequent corrective action which must be taken to return the apparatus to acceptable operating conditions tend to increase the cycle time for wafer manufacturing.
In a conventional coolant supply circuit arrangement, an input voltage of about +15V, for example, may be used for setting a desired coolant mass flow. In an exemplary system, such an input may be intended to regulate the mass flow of coolant at about 30 standard cubic centimeters (sccm), for example, per unit time. As noted above, however, the flow or the pressure of coolant is generally not constant and may spike abruptly. FIG. 1 is a graphical representation indicating the mass flow of helium coolant as a function of time in such a conventional system. In FIG. 1, time (in seconds) is measured along the abscissa, while the mass flow of helium (in 10xe2x88x922 sccm) is represented by the ordinal value. As indicated by the two spiking dotted lines 12 and 14, and by noise spikes 12xe2x80x2 and 14xe2x80x2, the helium flow is not uniform.
The cooling system of the present invention overcomes the foregoing and other shortcomings of conventional systems which suffer from fluctuating coolant mass flow rates or pressures.
In accordance with one aspect of the invention, a cooling system may be used in conjunction with an etching chamber, and may supply a wafer inside the etching chamber with coolant during an etching process. The inventive cooling system may generally be constituted by a printed circuit board, a coolant flow controller having a setpoint control to set a flow of coolant by transmitting a voltage signal to the printed circuit board, and a filter for removing undesirable noise from the voltage signal to stabilize the flow of coolant.
In accordance with another aspect of the present invention, an apparatus for manufacturing semiconductor devices may include an integrated cooling system. The apparatus may generally be constituted by a reaction chamber for performing a semiconductor process on a wafer therein and a cooling system for supplying a flow of coolant to the wafer during processing. The apparatus may include a structure or mechanism for controlling a flow of coolant used to cool the wafer when the semiconductor fabrication process is performed, wherein the structure or mechanism for controlling has a setpoint control to set the flow of coolant by transmitting a voltage signal to a printed circuit board, and may further incorporate a mechanism for removing undesirable noise from the voltage signal.
The foregoing and other attendant advantages of the present invention will become more apparent to those of ordinary skill in the art upon examination of the following detailed description of embodiments thereof with reference to the drawings.